1. Field of the Invention
The present invention relates to a pumping unit for actuating a down hole pump for pumping fluid, primarily crude oil, from subterranean oil-bearing formations to the earth's surface. More particularly, the present invention relates to a pumping system that includes a sampson post extending upwardly from a base supported on the earth's surface, a walking beam pivotally supported by a saddle bearing at the sampson post upper end with a horsehead affixed at a forward end of the walking beam to receive the upper end of a downwardly extending sucker rod string by which a subsurface pump is vertically reciprocated, the system including a gear reducer mounted on the walking beam for rotating a crank arm. The crank arm has affixed at the outer end thereof a crank pin bearing which secures one end of a pitman rod, the opposite end of the pitman rod being affixed by a pitman bearing to a variably pitman bearing location relative to the sampson post by which the characteristic of the pumping unit upward work strokes and downward return strokes can be selectably varied.
2. Prior Art
A primary source of energy as used by the world today is derived from crude oil. Oil-bearing formations deep below the earth's surface are the source of crude oil. Bore holes are drilled from the earth's surface downwardly to penetrate crude oil producing formations. In some parts of the world such formations have sufficient formation pressure that crude oil is forced to the earth's surface in which case the crude oil is recovered without being pumped. In other parts of the world formation pressures are insufficient to force the crude oil to the earth's surface and therefor the crude oil must be pumped. In many instances when a formation is initially penetrated the formation pressure causes the crude oil to flow to the earth's surface but after a time as quantities of crude oil are removed from the formation the formation pressure drops so that it then becomes necessary to pump the crude oil to the surface.
Various systems exist for pumping crude oil from a subterranean formation including hydraulic pumping systems, electric pumping systems in which a motor rapidly rotates a centrifugal pump, and so forth. However, the most commonly used system for extracting crude oil from a producing formation is by the use of a reciprocating string of sucker rods that extend within a bore hole from the earth's surface to a positive displacement, reciprocating pump. At the earth's surface a system must be provided for sequentially reciprocating the sucker rods in up and down fashion. The most common mechanism for performing this work is referred to as a pumping unit. The common type of pumping unit includes a base mounted on the earth's surface. Upwardly extending from the base is a post, sometimes referred to as a sampson post. At the top of the sampson post is a saddle bearing that pivotally supports a walking beam. The walking beam has at one end a “horsehead” that receives a wire line or cable that passes over a convex outer face of the horsehead, the outer face being curved with reference to saddle bearing as pivotal axis of the walking beam. The wire line connects at its lower end to the upper end of the string of sucker rods. The sucker rods are vertically reciprocated by the pivotation of the walking beam in a vertical plane.
Various systems have been devised for providing the pivotal action of a walking beam supported on a sampson post to achieve the reciprocal action necessary to move sucker rods to actuate a bottom hole pump. The invention herein relates to such a system.
A typical bottom hole pump includes a piston vertically reciprocating in a cylinder, the piston being connected to the sucker rod string so that as the horsehead of the pumping unit is pivoted the sucker rods move the pump piston in an oscillatory cycle. The upward movement of the sucker rods caused by the pivoting walking beam is usually termed a “work stroke” and downward movement that permits the pump piston to return to the lower part of the pump barrel as referred to as a down or “return stroke.”
Various means have been devised for reciprocating the walking beam. Further, it is important that the walking beam be counterbalanced to counteract the huge weight of the string of sucker rods that extend from the earth's surface. The length of a string of sucker rods may vary from a few hundred feet to a few thousand feet and accordingly constitute a substantial weight. Further, as the sucker rod string is moved upwardly, the column of fluid within the well bore hole is simultaneously moved upwardly to elevate the fluid to the earth's surface that constitutes the well's production.
The typical, that is the most common pumping unit, employs a gear reducer mounted on a slab or base that rests on the earth's surface. The gear reducer has a horizontal rotating shaft extending therefrom. A crank arm has one end affixed to the rotating shaft. At the other end of the crank arm is a bearing that receives the first end of a pitman rod. The second or upper end of the pitman rod is affixed to the walking beam. Rotative energy is supplied by a prime mover to the gear reducer to rotate the crank arm and thereby oscillate the pitman rod to cause the pumping unit walking beam to pivotally reciprocate in a vertical plane.
This typical type of pumping unit requires substantial counterbalancing. For this reason, weights are affixed to the walking beam to help offset the weight of the sucker rod string plus the weight of fluid being lifted. Many pumping units in use today include dynamic counterbalance weights that rotate with the crank arm. Properly designing and operating a pumping unit, particularly for a deep well, is an exacting science.
A complicating factor with respect to a pumping unit design is caused by the elasticity of the sucker rod string. That is, as the pumping unit pivots to lift the sucker rod string and accordingly the weight of the column of fluid in the well bore hole, the sucker rods stretch due to the elasticity of the steel or other metal alloys of which the sucker rods are constructed. When the sucker rods are in the downward or return stroke mode the sucker rods contract. The extension and contraction of a sucker rod string can introduce complex standing wave phenomena that must be taken into consideration in the design and operation of pumping units, especially for deeper wells.
Much creative work has been done in designing pumping units. The American Petroleum Institute has published works relating to the design and operation of pumping units entitled, “API Specification For Pumping Units, American Petroleum Institute, Washington D.C.” and issued by the American Petroleum Institute Production Department, 211 N. Irvay, Suite 1700, Dallas, Tex. 75201. This document was published in 1984 and is a standard reference for those engaged in designing and operating pumping units.
For reference to prior issued United States patents that provide a good background relating to the subject matter of pumping units and therefore specifically relating to the subject of this invention, reference may be had to the following previously-issued United States patents:
U.S. Pat.No.InventorTitleIssue Date4,660,426MosleyPUMPING UNIT FORApr. 28, 1987ACTUATING A DOWNHOLE PUMP WITHSTATIC AND DYNAMICCOUNTERWEIGHTS1,986,012PattersonPUMP ACTUATINGJan. 1, 1935MECHANISM4,603,592SieboldOFF-VERTICALAug. 5, 1986et alPUMPING UNIT2,958,237JohnsonSTROKE ADJUSTINGNov. 1, 1960MECHANISM4,505,162Hoh et alOIL WELL PUMPINGMar. 19, 1985APPARATUS AND METHOD5,105,671SlaterWELL PUMPING UNITApr. 21, 1992WITH ADJUSTABLEBALANCE BEAM4,502,343DingfelderPUMP JACKMar. 5, 19853,371,554McCrayINTEGRAL CRANK ANDMar. 5, 1968et alPHASEDCOUNTERWEIGHT ARM2,294,094O'LearyCOUNTERBALANCEDAug. 25, 1942PITMAN GEARING